Nickel anode



Ded 1 'c. GUBIEBER ET AL 2,304,059

NICKEL ANODE Filed Oct. 16, 1939 A TTORNE Y Patented Dec. 8, 1942 UNITED STATES, PATENT OFFICE moxnr. snoop Clarence George Bleber and Harry E. Techop,

Huntington, W. Va... assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware I Application October 16, 1939, Serial No. 299,582

1 Claim.

come these technical problems. One of the problemsof nickel electroplating has been the accumulation of sludge from the anode in the electroplating bath. The most generally used means of overcoming this diiiiculty in the past has been the use of anode bags or their equivalent. However, the use of anode bags has not completely solved this problem, particularly in view of the fact that these bags, which are 'usually made,

from textiles, tend to disintegrate in the plating bath and thus fail in their purpose.

Another operating dimculty which has confronted the practical electroplater has been the problem of obtaining satisfactory and uniform corrosion of. the nickel anode. Many years ago it wasdemonstrated that the passivity of conventional nickel anodes of commerce could be eliminated in various ways. For example, as early as 1924 Thomas and Blum showed that the .passivity of nickel anodes could be overcome by incorporating sufficient carbon in the anode to provide an anode having at least 0.4% carbon up to 11.4% or more. [See Trans. Electrochemical Soc., vol. XLV, (1924) 193-218]. These investifactory and practical manner the outstanding problems confronting the electroplater of nickel on a practical and industrial scale.

It is an object of the present invention to provide nickel anodes of enhanced.activity.

It is another object of the present invention to providera nickel anode producing less loose nickel than anodes heretofore available to the art.

It is a further object of the present invention to provide a nickel anode producing less sludge.

than prior nickel anodes.

It is still a further object of the present inventlon to provide a nickel anode producing less sludge than conventional nickel anodes.

It is also within the contemplation of the present invention to provide a nickel anode tending to maintain the desired operating pH of the electrolyte for greater periods of timethan anodes well known in the art.

The present invention also contemplates the provision of a nickel anode having enhanced activity, uniform corrosion, a reduced tendency to produce loose nickel, and a reduced tendency to produce 'free sludge, and being capable of maintaining the desired operating pH of a nickel plating bath for greater periods of time than prior nickel anodes. 7

Other objects and advantages will become apparent from the following description taken in conjunction with the drawing which is illustrative of a graph showing the relation between gators observed that at a carbon content of 1.4%-

designed, nevertheless none of these additions of individual elements provided the solution of all of thedimculties confronting the electroplater. Thus",-'so far as we are aware, the art has not been' provided with a nickel anode having a special combination of addition elements in critical proportions "and percentages which solved in a satisthe amount of graphitic \carbon present. in a nickel anode and the amount of loose nickel produced upon corroding the anode in a conventional electrolyte.

Broadly stated, a nickel anode prepared in accordance with the principles of the present invention contains as its major constituents nickel and cobalt. As addition elements for control of sludge, loose nickel, uniformity of corrosion, and equilibrium pH,,carbon,' sulphur, silicon, copper and magnesium are present within certain critical limits and the elements manganese and iron are maintainedat as low a level as is consistent with practical operation. I

In order to provide those skilled in the art with a better appreciation of the effect of the various elements upon the physical and electrochemical characteristics of our improved nickel anode, a consideration of the eflect of each separate element upon all of these characteristics and the relation of each element to the other elements in the combination can best be presented by considering the efiect of each separate element upon these characteristics.

Our improved nickel anode may have the to lowing composition:

Per cent (about) -.35

Mn .001-.010 Fe .02 -.10

S .001-.020 Si -.50 Cu .01 -.l0 Mg 02 -.15 Ni plus Co Balance While nickel anodes having the composition given hereinbefore have been found satisfactory, we prefer to maintain the composition within a narrower range substantially as given hereinafter.

C About .-about- .30% Mn Less than 003% Feud Less than .05%

S About .007-about .010% Si About .20-about Cu .About .03-about .04 Mg About .05-about .07% Ni plus Co-.- Balance As will be readily appreciated from the foregoing, the carbon content of our improved nickel anode ma be controlled within the broad range of about 0.15% to about 0.35% with a preferred carbon content of about'0.20 to about 0.30. While it is old in the art to prepare nickel within the critical limits indicated hereinbefore appear to develop a .film or coating on the surface of the anode during corrosion which appears to act as a filter and collecting medium. Such a film or coating holds and retains any loose nickel or other undesirable particles which may cause rough plating. In addition, this film adheres to the surface of the anode rather tenaciously and, when it finally breaks off, falls to the bottom of the tank as comparatively large pieces and carries with it these objectionable particles. Thusjthe addition of carbon within the critical limits heretofore mentioned practically eliminates this source of rough plating and consequently is of considerable value to the practical plater. In addition to this advantage the control of the carbon content of our new nickel anode permits it to corrode smoothly at higher pH values. Thus, as will be readily appreciated from Table 1, two nickel anodes in which sulphur, silicon and magnesium were maintained constant, while the total carbon content varied from about 0.09% to about 0.51%, were compared for the limit of activity for each anode.

The pH at which the anode containing a small amount of carbon reached its limit of activity was pH 3 while the anode containing the larger amount of carbon did not reach its limit of activity until a pH of about 3.4, as determined by, the quinhydrone electrode, was reached.

As those skilled in the art know, the expres-- sions limit of activity, or upper limit of activity,

'or activity limit are regularly used in the electroplating industry. It has always been customary for distributors and. platers to designate the pH at which the surface of the anode starts to corrode roughly or unevenly, leavinga pitted or lacy surface or the pH at which loose metallic par-.

ticles could be brushed or removed from the surface as the upper limit of activity, limit of acat a high anode efiiciency and therefore is not passive. In Table II are given the anode and I cathode efficiencies of a number of anodes at the upper limit of activity. It will be seen .by an inspection of Table II that even at the various hydrogen ion concentrations indicated as the upper limit of activity the anode and cathode efliciencies are still high which indicates that the anodes in question still were furnishing nickel to the bath. Nevertheless if these anodes or similar ones are operated above this "activity limit, the surface of the anodes will become rough and excessive amounts of loose metallic particles will be given 011. Such anodes having relatively low upper limits of activity would not be acceptable to the trade from a surface standard even although good anode efliciencies would still be obtainable. Therefore the improved characteristic of our novel anodes to wit; upper limit of activity, etc., is to be interpreted in the manner generally accepted by the art.

Table II Uppeililnit Anode Cathode H g g tg efficiency efliciency Per cent Per cent 3. 0 99. 7 5 3. 9 97. 5 99. 3 4. 4 99. 9 99. 4 4, 8 98. 3 99. 5 5. 5 97. 7 6

While the pH of the limit of activity may be pushed toward the alkaline side by the addition of carbon, such additions cannot be made within the metal since it has been found that pre-- cipitated carbon or graphitic carbon increases the amount of loose nickel formed during the As will be seen from the graph of'Fig. 1 after annealing for one hour the amount of carbon present as" graphite in the anode. represented about 3.4% of the total carbon present. At the end of three hours the relative amount of graphitic carbonihad increased approximately 600% while at the end of '7 hours annealing the graphitic carbon had increased to an amount approximately 2100% of that present at ,the end of a one hour period of annealing. The total car- -bon present in the anode subjected to the various annealing periods was 0.29% and the amount of graphitic carbon increased from 0.01%

at the end of annealing for one hour to 0.21% at the end. of a 7 hour annealing period. It is therefore important that in the fabrication of our improved nickel anode that the anode should be quenched or cooled rapidly after hot rolling to minimize the formation of graphitic carbon.

Carbon also-influences the behavior of the anode during corrosion by its effect on the adherence of the sludge to the surface of the anode.

If the carbon content of the anode is too low tanks operating without anode bags, nevertheless even in tanks in which the anodes are bagged, it is not unsual for the bags to disintegrate due to high acidity. and chlorine evolution. During operation also it is not unusual for anode bags to be torn. Consequently, it will be readily understood that whether the plating operation be carried on with or without anode bags, the possibility of the escape of sludge from the conventional anode is an ever present source of difliculty which is overcome by the critical control of the carbon content in our improved nickel anode. An additional efiect of carbon which must be taken into consideration in determining the critical limits of the carbon content of a nickel anode is the fact that in the presence of excessive amounts of carbon, excessive amounts of sludge are produced whichlower the useful nickel content of the anode.

The presence of sulphur in nickel anodes is attended by undesirable, as well as beneficial effects. Too great an amount of sulphur results in the building up of large undesirable amounts of loose nickel with theirattendant drawback. Onthe' other hand, sulphur has an appreciable influence on the activity of the anode and on its sludge adherence. Anodes which contain an insumcient amount of sulphur corrode very smoothly with the result that the sludge is more readily detached during interruptions in plating. On the other hand, the presence of small amounts of sulphur in the anode cause it to corrode in such a manner as to leave a slightly rougher matte surface which is conducive good sludge adherence.

Ithas been found that anodes which donot contain any sulphur cannot be made active at a pH of about 4.0 or higher without increasing the content of other elements to a point at which these other elements cause detrimental eflects.

The effect of sulphur in increasing activity may be readily seen in the following tabulation:

Table III To- Ni Activfig 051 3 Fe s Si 011 plus Mg ity at C 00 4.0 pH

1.. .25 .01 .05 None .23 .05 99.34 .056 Poor.

added 2. .25 .01 .05 None .22 .03 99.38 .057 Do.

added a..- .25 .01 .05 .007 .24 .00 00.33 .osa e000. 4..-. .25 .01 .05 .011 .22 .04 00.35 .051 D0.

' In evaluating the results set forth in the foregoing table it will be observed that the four heats considered therein had very nearly identical chemical analyses except for the sulphur content.

Although sulphur is very desirable in obtaining good activity at a pH of about 4 or higher, nevertheless the addition of too much sulphur is to be avoided since it appears that a sulphur content greater than a critical amount affects the production of loose nickel. Thus, as will be seen in Table IV, a sulphur content exceeding about 0.010% results in the formation of excesiive amounts of loose nickel.

Table IV 1* 051 o 11 Ni t o rap cen Heat No. C Re 8 Si Mg Fe pg izs loose nickel fold efiect upon the physical and electrochemical characteristics of nickel anodes. While the activity of a nickel anode substantially devoid of silicon can be maintained at a pH of about 4.0 by

the addition of major amounts ofcarbon and sulphur, such additions are undesirable as will be readily understood from the foregoing discussion of the effect of carbon and sulphur. Consequently, in order to raise the pH limit of activity without incurring the disadvantages attendant upon the addition of comparatively large amounts of carbon and sulphur, silicon is added to our improved nickel anode. The effect of silicon in increasing the activity can be appreciated by aconsideration of the following tabulation:

Table v Activ- 0 Fe s at Cu Mg 52' For a proper appreciation of the effect of silicon upon the upper limit of activity of a nickel anode attention is directed to the fact that the first twoheats tabulated in Table V have approxi-' mately the same composition except for the variation in silicon content. The last three heats while having a higher carbon content than the first two nevertheless were practically identical exceptfor the silicon content. the behavior of the anodes within these two groups shows the extent to which silicon influences the upper activity limit.

In addition to raising the upper activity limit silicon likewise improves sludge adherence. It may be assumed that due to the gelatinous nature of the silicon combination (such as hydrated formsof $102) which is formed or preci'pitated during anode corrosion, the sludge tends to hold together in a fairly compact mass. This compact mass adheres more firmly to the surface of the anode during corrosion. This effect of silicon taken in conjunction with the sim-- ilar efiect of carbon entraps any loose nickel and other undesirable particles and reduces the tendency or, in fact, practically eliminates the tendency of free particles migrating to the cathode and producing a rough plating. Of course, it is to be appreciated that all of the silicon in the anode does not appear in the sludge. Depending upon the acidity of the solution and the silicic acid content thereof, a greater or smaller proportion of the silicon dissolves in the electrolyte. In solutions operating at a low pH, and when anodes containing silicon are corroded in a new or purified solution, substantially all of the silicon will pass into the solution. As the concentration of the silicic acid builds up in the electrolyte the percentage which remains in the sludge increases.

Silicon when present in nickel anodes within critical limits has a most remarkable and advantageous efiect upon the equilibrium pH of the solution. As those skilled in the art know, under any given set of operating conditions the pH of the electroplating bath will tend to attain a definite value. At this definite value the anode and cathode efliciencies are substantially the same. In other words, at equilibrium conditions an electroplating bath remains automatically at a substantially constant composition and at practically the same pH. While it is well known .that the equilibrium pH depends on several factors including temperature, cathode current density, and composition of the solution, nevertheless We have found that the presence of silicon in the anode influences the equilibrium pH to a pronounced degree. By choosing an anode with the silicon content within the critical limits set forth hereinbefore, it will be possible in practical operations to maintain the electroplating solution at the proper pH level without the necessity of frequent chemical checks and, consequent correction of the solution. Since it is easier to lower the pH of a solution or, in other words, make it more acid, than it is to raise the pH or make it more alkaline, it will be appreciated that it is generally desired that the equilibrium pH be slightly higher than the pH at which the solution is intended to be operated. In accordance with the principles of the present application an anode tending to maintain an equilibrium pH slightly higher than the desired operating pH of the plating solution will be selected.

We have found that if the silicon content be much below 0.15%, it is diflicult to obtain satis- Comparison of factory activity and sludge adherence. On the other hand, if the silicon content is much above about 0.30% the equilibrium pH will be lower than is usually desirable for most electroplating operations. In addition, if the silicon content is too high, the purity of the anode naturally is decreased and the silicon content of the solution builds up so rapidly that the solution has to be purified more frequently.

A consideration of the following table will make it apparent to those skilled in the art that the equilibrium pH is affected to a very noticeable extent by increasing amounts of silicon and it can be readily seen that the equilibrium pH varies approximately inversely with the silicon content.

Table VI Per Equig g cgnt librium 0 Mn Fe 5 Cu Ni Mg .01 5.1 .14 .08 .l4.005 .0499.56 Notdet. 02 5. 3 56 Trace 08 005 02 99. 29 Not dot. .02 5.0 .51 Trace .l9.005 .1199.09 .05 .02 5.1 .09 .ll.005 .0399.62 .04 .17 4.3 .54 Trace .14.009 .0498.96 .07 .18 4.3 .31 Trace .07.019 .02 99.29 .09 .19 4.1 .27 Trace .l3.023 .0299.28 .07 .19 4.2 .31 Trace .25.008 .0299.l3 .07 .20 4.3 .35 Trace .03.005 .0l99.38 .08 .27 3.2 .41 Trace .05.005 .02 99.13 .09 .31 3.0 .47 Trace 03 005 .02 99. 09 08 .35 2.9 .10 Trace .09.02l .02-.9940 Notd .36 2.4 .05 Trace .08.005 .0599.43 .09 41 2.0 .54 Trace 06.005 .02 98. 84 10 .67 2.6 .22 .10 .10.014'.0198.91 Not det.

A study of Table VI makes it manifestthat nickel anodes can be produced which will maintain the equilibrium pH of an electrolyte substantially constant at a predetermined value.

For example, the electrodes, the analyses of which are tabulated as items 1, 2, 3 and 4 of Table 6, include both rolled and cast anodes having different percentages of carbon, iron, and copper. Nevertheless, with a silicon content practically identical in all four, the equilibrium pH is practically constant. Similarly, if the anodes, the analyses of which are tabulated as items 5 to 9 of Table VI be considered, it will be observed that for a'silicon content of from about 0.17 to about 0.20, the equilibrium pH is about 4.2- *0.1 of a pH unit, even although the carbon content, the percentage of iron and copper vary considerably. The anodes, the analyses of which are tabulated as items 10, 11 and 12, whether rolled or cast, maintain the equilibrium pH at about pH 3.0 i about 0.1 pH unit when the silicon content varies between about 0.27 and about 0.35% silicon, even although the carbon content varies from about 0.10% to about 0.47%. As is clearly shown in items l3, l4 and 15 of Table 6, a

silicon content of 0.36 or more provides a nickel anode capable of maintaining an equilibrium pH of about 25:0.1 pH unit. This condition exists even in the. presence of a large variation in the carbon content. It is of interest to note in connection with anodes l3, I4 and I5 that an increase in the silicon content above about 0.36 does not affect the equilibrium pH to any great extent. This analysis of the effect upon the equilibrium pH of an electrolyte of the silicon content of a nickel anode clearly shows that in the presence of varying amounts of other elements 2. control of the silicon content of the anode provides a means of controlling the equilibrium pH of the electrolyte at any determined level, Thus, by choosing an anode with the proper silicon content it will be possible for the electroplater to maintain his solution at the proper pH level without the necessity of frequent chemical checks of the electrolyte composition followed by correction of the solution.

We have found that the addition of magnesium in critical amounts is an important factor in controlling the physical characteristics of nickel anode. -While sulphur improves the corroding characteristics of a nickel anode, un-

bound sulphur or free sulphur tends to increase the amount of loose nickel given ofi during the corrosion. The amount of loose nickel given off during the corrosion of an anode containing anpreciable amounts of unfixed sulphur may reach a value as high as of the weight of the disl8 solved metal. However, this undesirable characteristic of nickel anodes containing'sulphur in the free state may be practically, eliminated by the addition of magnesium within the critical derived. In other words, our improved nickel anode is tailored to meet the exacting conditions of modern nickel electroplating practice.

Although the present invention has been described in conjunction with satisfactory particular embodiments thereof, it is to be understood that variations and modifications may be made, as those skilled in theart will readily appreciate.

Such variations and modifications are to be con-- sidered within the purview of the specification and the scope of the appended claim. Thus, the improved nickel anodes described hereinbefore while having compositions within the critical ranges set forth may be rolled or cast. Furthermore, it is preferred to produce the anodes described herein by forging and rolling in order to ensure the production of anodes free'from blowholes, pipes etc.. and having afiner, more uniform grain size.

limits set forth hereinbefore. However, it is to 20 We claim:

be appreciated that if the magnesium content .is too high, the activity'of the anode decreases somewhat.

While the exact effect of copper in our improved nickel. anode has not been determined definitely, it is believed that within the critical limits set forth hereinbefore, copper increases the activity of the anode.

In view ,of the fact that the opinion is quite prevalent in the electroplating art that mangaso nese and iron are detrimental to the corrosion resistance of nickel plating we attempt to maintain the manganese and iron content of our 1111-. proved anodes at as low a value as possible.

From the foregoing those skilled in the art will 35 readily appreciate that the various elements carbon, sulphur, silicon, magnesium and copper cannot be added haphazardly if the novel results obtained by us are to be the standard characteristics 'of our new and improved nickel anode. 40 v To obtain the beneficial eflects of each of these elements without suffering the drawbacks of the detrimental effects attendant upon adding these elements in the quantities taught by the prior art,

'and to obtain the full benefit derived from our new and novel combination, it is necessary to maintain the percentage composition of the I nickel anode substantially within the ranges noted hereinbefore. In this manner each of these elements is added in such concentrations as approach very closely the borderline between the amount of the particular element which provides beneficial effects without detrimental effects and those concentrations of that elementwhich produce detrimental effects far outweighing benefits tive in conjunction with said carbon to promote good activity at pH higher than about pH 4; 0.20% to 0.25% silicon, saidsilicon being efiective in conjunction with saidcarbon and said sulfur to promote good activity at pH above about pH 4 but insuflicient to lower the equilibrium pH of nickel electroplating baths below that pH desirable for conventional nickel electroplating; 0.05% to 0.07% magnesium, said magnesium being effective in conjunction with said sulfur to avoid the production ofsignificant amounts of unbound sulfur thereby reducing the amount of loose nickel produced during corrosion; not more than 0.10% copper; not more than 0.01% manganese; not more than 0.10% iron and the balance principally nickel; said anode having increased activity, more uniform corrosion, a

greater sludge adherence and a lesser tendency to produce loose nickel than conventional carbon containing nickel anodes.

:.CLA1 ?;ENCE GEORGE BlEBER. HARRY E. 'rscnor. 

